As man roams the globe, from climbing high mountains to exploring ocean depths, increasing instances occur of detrimental effects of acute or chronic exposure to altitude or to reduced ambient pressure. A variety of acute, subacute and chronic conditions related to brief or prolonged exposure to altitude (or to decompression, in the case of divers and others working at elevated pressure) are nevertheless alleviated by treatment in a hyperbaric atmosphere. (The term "hyperbaric" is used herein to mean a pressure greater than ambient, over and above the range of pressure variation encountered in the course of normal fluctuations in atmospheric pressure caused by changes in the weather.)
It is well-known that humans ascending to altitude may experience a variety of symptoms collectively known as "mountain sickness." The symptoms of mountain sickness are especially prevalent with people coming from sea level to ski at ski resorts 2000 meters and higher above sea level. In general, these symptoms are not severe and after a few days of nausea and headache the symptoms go away. Nevertheless, some individuals are dreadfully sick even at these low altitudes, and it would be beneficial to get them to a higher barometric pressure as soon as possible.
On the other hand, severe mountain sickness which includes the following diseases: acute mountain sickness, high altitude pulmonary edema, Monge's disease and Brisket disease, are of major concern of mountaineers. The problems for mountaineers are of course very much greater than for the recreational skier. First, the altitudes may be very much greater, approaching 10,000 meters, and the physical condition of the climbers themselves is greatly weakened not only from the altitude but from the long-term exposure to extreme elements. All life supporting systems must be carried by foot and be contained in backpacks. To date, if a climber becomes severely ill because of the altitude the only treatment is to get him or her to as low an elevation as possible as soon as possible. This is often not done because weather and terrain conditions may trap the climbers for days, if not weeks.
A second problem that mountaineers experience at altitude is the inability to maintain a regular sleep cycle. This problem is more severe for some climbers than others, but it is a problem for every high altitude climber.
In addition to detrimental effects which may be hazardous to health, changes in altitude are known to affect athletic performance. It is well-known that persons who normally live at or near sea level experience such symptoms as shortness of breath and dizziness when they travel to high altitudes. The symptoms usually wear off in one to two weeks. Such experiences have been explained as being the result of reduced ambient oxygen tension in high altitude air (See Abstracts, International Symposium on the Effects of Altitude on Physical Performance, Mar. 3-6, 1986, Albuquerque, N. Mex.). Initial acclimatization has been shown to be accompanied by an increase in circulating red blood cells presumably put into circulation to enhance the blood's oxygen-carrying capacity (Ibid.). Full acclimatization is achieved after 2-3 months, and is accompanied by an increased hematocrit.
It has been recommended (Castro, R., "Altitude Offers Big Training Advantage," Boulder Daily Camera, Sep. 14, 1978) that athletes engaged in sports such as running, cycling and the like, where a high level of cardiovascular output is required, should train at altitudes. It is generally accepted by athletes that altitude training is beneficial (see Williams, K., "Boulder is Training Haven for Runners," Boulder Daily Camera, Apr. 22, 1985). The recommendation is based on the rationale that the normal acclimatization to altitude will generally improve cardiovascular efficiency, and hence athletic performance.
Practical application of the foregoing rationale has not been demonstrably successful. Many athletes trained at altitude prior to competing in the 1968 Olympics, held in Mexico City (7,500 feet). Even with this altitude training, no new records in track endurance events were set that year (Daniels, J. and Oldridge, N. (1970) "The effects of altitude exposure to altitude and sea level on world class middle distance runners" in Medicine and Science in Sports, Vol. 2, No. 3, pp. 107-112). Recently evidence has been reported that casts doubt on the notion that athletes who have lived and trained at altitude would have an advantage in terms of performing endurance events at altitude or near sea level (Grover, R. F. et al. (1976) Circulation Res. 38:391-3). Grover has shown that the total volume of blood declines by as much as 25 percent as the body responds to high altitude. This decrease in blood volume causes an increase in blood viscosity that, in turn, causes the heart to decrease the amount of blood pumped. Since endurance athletic performance is thought to be dependent on the amount of oxygen in the blood, a decrease in blood volume might result in a decrease in athletic performance. This decrease in plasma volume results in the well-known phenomenon of measuring an increase in red blood cell concentration (hematocrit) as a result of acclimatization to altitude. Doctors who work in the field of sport medicine have long known that athletes have a condition known as sports anemia (Pate, R. R. (1983) "Sports Anemia: A Review of the Current Research Literature" in The Physician and Sports Medicine, Vol. II, No. 2). They appear to have fewer red blood cells, but in reality they have an increase in plasma volume. One interpretation is that this increase in plasma volume allows the heart to perform to its maximum ability, thereby increasing athletic performance.
The present invention provides a unique device, a portable hyperbaric chamber, adapted in various ways to provide a temporary environment of elevated pressure. The device is described with respect to specific adaptations thereof, in order to demonstrate certain new uses, not heretofore available. In one embodiment, the device serves as an exercise environment, permitting an improved endurance training regimen. In another embodiment, the device is adapted for the emergency treatment of "mountain sickness" or acute pulmonary edema. The disclosed uses are novel, no previous device being available to perform the functions of the device of the present invention.
While not based upon any specific theory or hypothesis, the present invention provides in one embodiment a novel and unobvious method of endurance conditioning and apparatus for carrying out such a method which is consistent with the foregoing observations. This embodiment of the invention is based on the premise that, contrary to the widely held view that endurance training at altitude is beneficial to athletic performance, the opposite is in fact the case: athletic performance in endurance-type events is improved at all altitudes by undertaking the training exercises at an atmospheric pressure equal to, or even greater than, the normal pressure at sea level. The benefit of training at such pressures is obtainable by persons living at altitude, provided the training exercises are carried out at sea level or greater than sea level pressures. The invention includes the design and construction of a hyperbaric chamber that would allow an athlete living at altitude to train at or below sea level, either in his or her own home or in an athletic club.
Another embodiment of the invention described herein provides a unique solution to the alleviation of mountain sickness, pulmonary edema and sleep cycle disruption due to altitude by providing a portable hyperbaric chamber which can be folded or collapsed and carried in a backpack, to be deployed as needed to simulate a lower altitude for a climber suffering mountain sickness without moving the climber to a lower altitude.
Hyperbaric chambers of the prior art have been heavy, rigid structures, permanently installed. Any structure of rectilinear design must be constructed of extremely strong and heavy materials, even to maintain 10 pounds per square inch pressure greater than ambient. Structures with such design are permanently installed. Cylindrical chambers large enough to admit a human being and allow movement within the chamber have been disclosed (see, e.g., Wallace et al. U.S. Pat. No. 4,196,656), but such structures are not truly portable, which term is used herein to mean capable of being dismantled, packaged and carried by an individual person. Air-supported structures, tennis domes, radomes and the like are distinguished from the devices of the present invention by the fact that only a minuscule increment of pressure is needed to maintain such structures in an inflated condition. For example, a pressure differential of only 70 mm water pressure is all that is required to maintain the rigidity of a radar dome of 15 meter diameter in winds up to 240 mph. In units of psi, 70 mm of water is approximately 0.1 lb/sq. inch, an amount within the range of normal atmospheric fluctuations due to weather conditions and not hyperbaric as herein defined. Examples of air-supported, but nonhyperbaric structures are shown by Dent, R. M., Principles of Pneumatic Architecture (1972), John Wiley & Sons, Inc., New York; by Riordan, U.S. Pat. No. 4,103,369; and by Jones III, U.S. Pat. No. 3,801,093. Hyperbaric chambers of this invention are described in the following articles published after the priority filing date hereof, which articles are hereby incorporated herein by reference: R. I Gamow et al. (1990) "Methods of gas-balance control to be used with a portable hyperbaric chamber in the treatment of high altitude illness," J. Wilderness Medicine 1:165-180; S. J. King and R. R. Greenlee (1990), "Successful use of the Gamow Hyperbaric Bag in the treatment of altitude illness at Mount Everest," J. Wilderness Medicine 1:193-202; and R. L. Taber (1990), "Protocols for the use of a portable hyperbaric chamber for the treatment of high altitude disorders," J. wilderness Medicine 1:181-192.